1. Field of the Invention
The present invention relates to a variable compression ratio apparatus. More particularly, the present invention relates to a variable compression ratio apparatus that changes compression ratio of gas mixture in a combustion chamber in accordance with operational conditions of an engine.
2. Description of Related Art
In general, thermal efficiency of heat engines increases when compression ratio is high and when igniting timing increases to a predetermined level in spark ignition engines. However, the spark ignition engines have a limit in increasing the ignition timing because the engines may be damaged by abnormal combustion when the ignition timing is increased at high compression ratio, which necessarily reduce the output power.
A variable compression ratio (VCR) apparatus is an apparatus that changes compression ratio of gas mixture in accordance with operational conditions of the engine. According to the compression ratio apparatus, fuel efficiency is improved by increasing the compression ratio of gas mixture under the low load condition of the engine, and knocking is prevented and the engine output is improved by reducing the compression ratio of the gas mixture under the high load condition of the engine.
In order to achieve the variable compression ratio, an oil chamber is formed inside a bias ring disposed in a small portion of a connecting rod and the bias ring is eccentrically rotated by hydraulic pressure generated by supplying oil into the oil chamber, which has been proposed; however, the variable compression ratio apparatus according to the related art has a problem that the distance from the bias ring to the center of the oil chamber is small, such that pressure for maintaining the position of the bias ring in the oil chamber is largely increased when explosion pressure is applied, and it is difficult to maintain the compression ratio.
Further, there is a problem requiring excessive oil pressure, which is needed to change the compression ratio.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.